1. Field of Invention
This invention relates to clutches for motor vehicles and, in particular, to an improved design and application of frictional linings for enhanced performance of automotive clutches.
2. Brief Statement of the Prior Art
The typical automotive clutch has a clutch disc fixedly secured to the drive shaft and supported between the flywheel and a pressure plate. The clutch cover, which is bolted onto the flywheel includes a conical (Belleville) spring that is actuated by a clutch throw out mechanism and hydraulics to release the Belleville spring force against the pressure plate, clamping the clutch disc between the pressure plate and flywheel. The clutch disc supports frictional linings which usually have a metallic base ring on the theory that the high heat conductivity of a metal base ring would enhance heat transfer and thus reduce the tendency of the clutch linings to overheat.
The design of the present day automotive clutch is the result of a compromise of complex and competing design factors. Because of limitations in size and accessibility, and the requirement for a moderate pedal pressure, the maximum spring load which can be used with most clutches is from about 800 to about 2,000 pounds. The demand for increased performance of automobiles has increased the torque which is transmitted through the clutch and, accordingly, manufacturers provide clutches with clutch discs having diameters as large as practical to achieve moment arms adequate to handle the large torques transmitted by the clutches.
Most of the car manufacturers have elected to line the entire or substantially the entire face of the clutch disc with frictional linings, apparently on the theory of the more the better. This has resulted in the unit pressures applied to the clutch disc facings being approximately 25-30 psi.
Until the concern over the potential hazards to the public, asbestos-containing facings were the most commonly used facings. The phase out of asbestos facings has spurred development of new materials including in particular organic composite facings. These linings frequently have optimum unit pressures from about 35 to about 65 psi, or greater, which exceed the unit pressures of current clutch designs. This has caused a less than optimum performance of clutches, often observed as a chattering of the clutch, and high wear and maintenance of the clutch disc and its frictional facings. Further, the organic composite linings are particularly sensitive to high temperatures, loosing much of their performance when their temperatures exceed about 450 degrees F.
It is possible to improve clutch performance by increasing the size and strength of the Belleville spring, thus appearing a greater load to the clutch assembly. This approach, however, is not practical for a number of reasons. The clutches used in vehicles currently on the market have hundreds of differently sized and shaped Belleville springs and a conversion of even a small portion of the vehicles on the road and presently being manufactured would require many hundreds of thousand of dollars in tooling costs. Additionally, the higher loads imposed on the clutch assembly by the increased Belleville spring force would lead to higher thrust and would require substantially complete redesigning of the clutch throw out mechanism and hydraulics. Accordingly, the approach of increasing the load applied to a clutch is not a practical solution for retrofitting the millions of vehicles currently on the road or being marketed.
Car manufacturers also seek higher and higher performance, leading to a new type of car, the Street Legal Performance (SLP) car which has performance characteristics which rival those of the dragsters and race cars of recent years past. The traditional approach by car manufacturers has been to increase horsepower and torque dramatically and to retool the drive train including the clutch to handle the greater power and torque. Usually clutches have been upgraded by increasing the clutch diameter and/or clamp load. This approach is expensive and usually requires retooling of related mechanical equipment.
There exists, today, a need for a simple and efficient conversion to increase the performance of clutches, specifically by increasing the unit pressure applied to clutch facings to the optimum value which provides maximum performance of the particular frictional facings used in the clutch. There also exists a need for a clutch lining having a design and formed of materials which protect the facing from overheating.
It is an object of this invention to provide a clutch of superior performance.
It is a further object of this invention to provide a clutch conversion which achieves superior performance.
It is also an object of this invention to provide a conversion for current clutches, which is useful for retrofit or original manufacturer equipment, without retooling, and without requiring re-machining of the mechanical components of the clutch.
It is likewise an object of this invention to provide a conversion for a clutch that will achieve optimum unit pressures for the particular frictional facings used in the clutch without changing the other components of the vehicle and clutch.
It is an additional object of the invention to provide a conversion for an automotive clutch that increases the effective clamp load of the clutch to the optimum unit pressure for the frictional facings of the clutch.
It is likewise an object of the invention to provide a method for car manufacturers to provide cars which share common clutch components, but which have widely varied performance capabilities.
It is still a further object of the invention to provide a clutch lining of an improved design and materials which minimize the tendency of the facing to overheat, chatter or slip.
This invention includes a conversion for a clutch of a motor vehicle which uses a conventional Belleville spring to as a pressure plate and clamp a clutch disc between the pressure plate and the flywheel of the vehicle. In this invention, the frictional linings of the conventional clutch are substituted by frictional linings which are preferably located at optimum geometric spacing, and which have from 30-70 percent less surface area for frictional engagement than that conventionally furnished with the clutch. Preferably, the linings of the invention having reduced area facings are located adjacent the peripheral areas of the clutch disc to provide maximum movement arm for torque transmission. The reduced area linings are also provided with a hole pattern for attachment to the clutch disc which will utilize the existing hole pattern of the clutch disc thereby avoiding any machining or alteration of the clutch disc. In the most preferred embodiment, only the frictional lining on the flywheel side of the clutch disc is substituted with one having a reduced area facing thereby preserving the optimum heat sink on the pressure plate side of the clutch disc.
The invention is particularly applicable to upgraded performance cars, e.g., the new line of SLP cars being introduced by some manufacturers. Increased performance of the conventional clutch is achieved with the invention without the necessity to retool or resize the clutch components. In a preferred embodiment, the invention includes clutch linings having non-metallic base rings, which are formed of low heat transfer coefficient materials, such as fiber-rein forced plastics. This provides the manufacturer the capability of molding the facings and base ring in a single operation (integral), or molding the facing and bonding it to the base ring in a single operation. The molding of the facings in this manner permits the manufacturer to quickly change production between moderate and high performance clutch linings simply by switching mold dies or adding inserts to the mold dies used to shape the facings.